Any ad executive will tell you that sex sells. But why? Do sexy images stimulate our biological urges, somehow motivating us to buy products? Or do marketers merely exploit and perpetuate our cultural obsession with sexual imagery? Do people want the beauty, wealth and power celebrities have, and use the products they endorse in the hope of achieving these same qualities?

These explanations are plausible, but my colleagues and I have a new one, based on decades of work comparing the behavior and neurobiology of decision-making in monkeys and people: Our brains have been fine-tuned by evolution to prioritize social information, and this laser focus on others profoundly shapes our decisions.

As early as the 1870s, companies like Pearl Tobacco and later, W. Duke & Sons, employed social advertising, showcasing nude or partially exposed women on posters and trading cards. Although the images had no direct link to the products, sales increased. A century and a half later, it seems impossible to escape sexual imagery in advertising. The same is true for celebrities in marketing campaigns—actors, musicians, athletes, even politicians and business leaders. These celebrities often don’t even use the products they advertise, yet the method still seems to work.

Our brains have circuits specialized for identifying, remembering and inferring the mental states of others so we can predict their behavior and make good decisions. In other words, we’re built to deal with people. But we’re not alone in this connection. Many species of monkeys and apes—our closest living relatives—also live in large, complex, dynamic societies. Behavioral studies show that, like us, these primates identify others, track prior encounters, empathize with friends and relatives, and make inferences about individuals’ mental states.

For people and monkeys alike, it’s important to find a good mate, make powerful allies and avoid potential threats. Paying close attention to social cues can improve these choices. In fact, both men and male monkeys are exquisitely sensitive to indications of female fertility. Men rate ovulating women as more attractive, and tip more for lap dances by fertile women. Similarly, male rhesus macaques prefer images of females with artificially reddened faces and hindquarters, coloration that predicts ovulation and sexual receptivity.

Women and female monkeys are also sensitive to clues about male quality, although what we know about that is based on fewer studies. A woman’s preference shifts toward more masculine faces—broader jaw, wider-set but smaller eyes—during ovulation. Female macaques, when ovulating, tend to mate with higher-ranking males and prefer those with reddened faces caused by a testosterone surge. Other studies found that both people and monkeys pay more attention to high-status individuals and are more likely to follow their gaze.

According to economics, we can quantify how much someone values something—coffee, a magazine—by how much he or she will pay for it. In our latest work, we developed an assessment, dubbed the “pay-per-view” test, to measure subconscious value of visual images. In the experiment, monkeys had the option to forego juice or food for a glimpse at a picture of another monkey. People could choose whether to accept a smaller cash reward to peek at a picture of another individual.

Our findings were striking. Male college students paid slightly more money to view an attractive woman than an unattractive one, losing several dollars during the experiment. Female students were much less motivated to see attractive men. Monkeys of both genders valued sex and status, accepting less food or juice to see images of monkey genitalia and faces of high-status males. In contrast, they required extra food or juice to look at faces of low-status males.

Based on these findings, it’s clear that monkeys and humans value information about sex and status so much that it can replace rewards like food, juice and money. Strong parallels between the two suggest shared brain mechanisms at work.

To test this idea, we used fMRI to scan the brains of male students in two circumstances: one, while they viewed female faces of varying attractiveness, the other while money was either deposited or withdrawn from their study stipend. The sight of attractive faces strongly activated a network of brain areas previously implicated in processing rewards—including the orbitofrontal cortex, ventromedial prefrontal cortex, and medial and ventral striatum—and neural activity increased with increasing attractiveness. The same happened with monetary rewards and losses. We believe this network computes economic “utility,” a person’s internal desire for or satisfaction with a good or service, thought to underlie decisions.

To determine the physiological basis of these signals, we measured individual brain cell activity in monkeys. Some fired strongly when male monkeys chose to see female genitalia, a high-status male face, or a large juice reward, but fired less when they chose low-status faces or small juice rewards. Specific brain cells reacted to images of faces and genitals but not juice, indicating the brain’s reward system possesses dedicated hardware for identifying and prioritizing key social information.

Can these discoveries help explain the power of sex and status in advertising? In theory, ads that associate sex or status with specific brands or products activate the brain mechanisms that prioritize social information, and turning on this switch may bias us toward the product.

To test this idea, we exposed male rhesus macaques to logos of household brands like Nike and Pizza Hut paired with a social image (e.g., female genitalia, high-status male face) or the same image with pixels rearranged to make it unrecognizable but retain the same brightness, contrast, and color, salient cues that could draw attention to a stimulus. Monkeys received a sweet treat for touching the screen after the ad, then had the choice between brands paired with a social image or its scrambled version.

Our advertising campaign was remarkably effective. Monkeys developed preferences for brands linked with sex and status. Both males and females preferred logos paired with sexual cues and the faces of high-status monkeys. And the more often male monkeys saw sexual advertisements, the more they preferred the brands. Sound familiar? Even monkeys, it seems, can be persuaded to choose a brand through social advertising.

Given the nearly identical specializations of brain reward circuits to prioritize social information in monkeys and people, is it any wonder that sex and status sell?

People have evolved to sleep much less than chimps, baboons or any other primate studied so far.

A large comparison of primate sleep patterns finds that most species get somewhere between nine and 15 hours of shut-eye daily, while humans average just seven. An analysis of several lifestyle and biological factors, however, predicts people should get 9.55 hours, researchers reported recently in the American Journal of Physical Anthropology. Most other primates in the study typically sleep as much as the scientists’ statistical models predict they should.

Two long-standing features of human life have contributed to unusually short sleep times, argue evolutionary anthropologists Charles Nunn of Duke University and David Samson of the University of Toronto Mississauga. First, when humans’ ancestors descended from the trees to sleep on the ground, individuals probably had to spend more time awake to guard against predator attacks. Second, humans have faced intense pressure to learn and teach new skills and to make social connections at the expense of sleep.

As sleep declined, rapid-eye movement, or REM — sleep linked to learning and memory (SN: 6/11/16, p. 15) — came to play an outsize role in human slumber, the researchers propose. Non-REM sleep accounts for an unexpectedly small share of human sleep, although it may also aid memory (SN: 7/12/14, p. 8), the scientists contend.

“It’s pretty surprising that non-REM sleep time is so low in humans, but something had to give as we slept less,” Nunn says.

Humans may sleep for a surprisingly short time, but Nunn and Samson’s sample of 30 species is too small to reach any firm conclusions, says evolutionary biologist Isabella Capellini of the University of Hull in England. Estimated numbers of primate species often reach 300 or more.

If the findings hold up, Capellini suspects that sleeping for the most part in one major bout per day, rather than in several episodes of varying durations as some primates do, substantially lessened human sleep time.

Nunn and Samson used two statistical models to calculate expected daily amounts of sleep for each species. For 20 of those species, enough data existed to estimate expected amounts of REM and non-REM sleep.

Estimates of all sleep times relied on databases of previous primate sleep findings, largely involving captive animals wearing electrodes that measure brain activity during slumber. To generate predicted sleep values for each primate, the researchers consulted earlier studies of links between sleep patterns and various aspects of primate biology, behavior and environments. For instance, nocturnal animals tend to sleep more than those awake during the day. Species traveling in small groups or inhabiting open habitats along with predators tend to sleep less.

Based on such factors, the researchers predicted humans should sleep an average of 9.55 hours each day. People today sleep an average of seven hours daily, and even less in some small-scale groups (SN: 2/18/17, p. 13). The 36 percent shortfall between predicted and actual sleep is far greater than for any other primate in the study.

Nunn and Samson estimated that people now spend an average of 1.56 hours of snooze time in REM, about as much as the models predict should be spent in that sleep phase. An apparent rise in the proportion of human sleep devoted to REM resulted mainly from a hefty decline in non-REM sleep, the scientists say. By their calculations, people should spend an average of 8.42 hours in non-REM sleep daily, whereas the actual figure reaches only 5.41 hours.

One other primate, South America’s common marmoset (Callithrix jacchus), sleeps less than predicted. Common marmosets sleep an average of 9.5 hours and also exhibit less non-REM sleep than expected. One species sleeps more than predicted: South America’s nocturnal three-striped night monkey (Aotus trivirgatus) catches nearly 17 hours of shut-eye every day. Why these species’ sleep patterns don’t match up with expectations is unclear, Nunn says. Neither monkey departs from predicted sleep patterns to the extent that humans do.

Citations
C.L. Nunn and D.R. Samson. Sleep in a comparative context: Investigating how human sleep differs from sleep in other primates. American Journal of Physical Anthropology. Published online February 14, 2018. doi:10.1002/ajpa.23427.

wearing is usually regarded as simply lazy language or an abusive lapse in civility. But as Emma Byrne shows in her book, Swearing Is Good for You: The Amazing Science of Bad Language, new research reveals that profanity has many positive virtues, from promoting trust and teamwork in the office to increasing our tolerance to pain.

When National Geographic caught up with Byrne at her home in London, she explained why humans aren’t the only primates that can curse and why, though women are swearing more today than before, it is still regarded by many as “unfeminine.”

You write, “I’ve had a certain pride in my knack for colorful and well-timed swearing.” Tell us about your relationship to bad language, and in what sense it is good for us?

My first memory of being punished for swearing was calling my little brother a four-letter word, twat, which I thought was just an odd pronunciation of the word twit. I must have been about eight at the time; my brother was still pre-school. My mother froze, then belted me round the ear. That made me realize that some words had considerably more power than others, and that the mere shift in a vowel was enough to completely change the emotional impact of a word.

I’ve always had a curiosity about things I’ve been told I am not meant to be interested in, which is why I wound up in a fairly male-dominated field of artificial intelligence for my career. There’s a certain cussedness to my personality that means, as soon as someone says, “No, that’s not for you,” I absolutely have to know about it.

My relationship with swearing is definitely one example. I tend to use it as a way of marking myself out as being more like my male colleagues, like having a working knowledge of the offside rule in soccer. It’s a good way of making sure that I’m not seen as this weird, other person, based on my gender.

There’s great research coming out of Australia and New Zealand, which is perhaps not surprising, that says that jocular abuse, particularly swearing among friends, is a strong signal of the degree of trust that those friends share. When you look at the transcripts of these case studies of effective teams in sectors like manufacturing and IT, those that can joke with each other in ways that transgress polite speech, which includes a lot of swearing, tend to report that they trust each other more.

One of the reasons why there’s probably this strong correlation is that swearing has such an emotional impact. You’re demonstrating that you have a sophisticated theory of mind about the person that you’re talking to, and that you have worked out where the limit is between being shocking enough to make them giggle or notice you’ve used it but not so shocking that they’ll be mortally offended. That’s a hard target to hit right in the bullseye. Using swear words appropriate for that person shows how well you know them; and how well you understand their mental model.

You were inspired to write this book by a study carried out by Dr. Richard Stephens. Tell us about the experiment, and why it was important in our understanding of swearing.

Richard Stephens works out of Keele University in the U.K. He’s a behavioral psychologist, who is interested in why we do things that we’ve been told are bad for us. For years, the medical profession has been saying that swearing is incredibly bad for you if you’re in pain. It’s what’s called a “catastrophizing response,” focusing on the negative thing that’s happened. His take on this was, if it’s so maladaptive, why do we keep doing it?

He initially had 67 volunteers, although he’s replicated this multiple times. He stuck their hands in ice water and randomized whether or not they were using a swear word or a neutral word and compared how long they could keep their hands in ice water. On average, when they were swearing they could keep their hands in the iced water for half as long again as when they were using a neutral word. This shows that the results are anything but maladaptive. Swearing really does allow you to withstand pain for longer.

Have men always sworn more than women? And, if so, why?

Definitely not! Historians of the English language describe how women were equally praised for their command of exceedingly expressive insults and swearing, right up to the point in 1673 when a book by Richard Allestree was published titled The Ladies Calling.” Allestree says that women who swear are acting in a way that is biologically incompatible with being a woman and, as a result, will begin to take on masculine characteristics, like growing facial hair or becoming infertile. He wrote, “There is no sound more odious to the ears of God than an oath in the mouth of a woman.”

Today we are horribly still in the same place on men versus women swearing. Although women are still considered to swear less than men, we know from studies that they don’t. They swear just as much as men. But attitudinal surveys show that both men and women tend to judge women’s swearing much more harshly. And that judgement can have serious implications. For example, when women with breast cancer or arthritis swear as a result of their condition, they’re much more likely to lose friends, particularly female friends. Whereas men who swear about conditions like testicular cancer tend to bond more closely with other men using the same vocabulary. The idea that swearing is a legitimate means of expressing a negative emotion is much more circumscribed for women.

I was fascinated to discover that it’s not just humans that swear—primates do it, too! Tell us about Project Washoe.

Out in the wild, chimps are inveterate users of their excrement to mark their territory or show their annoyance. So the first thing you do, if you want to teach a primate sign language, is potty train them. That means, just like human children at a similar age, that they end up with a taboo around excrement. In Project Washoe, the sign for “dirty” was bringing the knuckles up to the underside of the chin. And what happened spontaneously, without the scientists teaching them, was that the chimps started to use the sign for “dirty” in exactly the same way as we use our own excremental swear words.

Washoe was a female chimpanzee that was originally adopted by R. Allen Gardner and Beatrix T. Gardner in the 1960s. Later, she was taken on by a researcher in Washington State called Roger Fouts. Washoe was the matriarch to three younger chimps: Loulis, Tatu, and Dar. By the time they brought in Loulis, the youngest, the humans had stopped teaching them language, so they looked to see if the chimps would transmit language through the generations, which they did.

Not only that: as soon as they had internalized the toilet taboo, with the sign “dirty” as something shameful, they started using that sign as an admonition or to express anger, like a swear word. When Washoe and the other chimps were really angry, they would smack their knuckles on the underside of their chins, so you could hear this chimp-teeth-clacking sound.

Washoe and the other chimps would sign things like “Dirty Roger!” or “Dirty Monkey!” when they were angry. The humans hadn’t taught them this! What had happened is that they had internalized that taboo, they had a sign associated with that taboo, so all of a sudden that language was incredibly powerful and was being thrown about, just like real excrement is thrown about by wild chimpanzees.

You say, “swearing is a bellwether—a foul-beaked canary in the coalmine—that tells us what our social taboos are.” Unpack that idea for us, and how it has changed over the centuries.

The example that most people will be familiar with in English-speaking countries is blasphemy. There are still parts of the U.S. that are more observant of Christianity than others but, in general, the kinds of language that would have resulted in censorship in other eras is now freely used in print and TV media. However, the “n-word,” which was once used as the title of an Agatha Christie book and even in nursery rhymes, is now taboo because there is a greater awareness that it is a painful reminder of how African-Americans suffered because of racism over the centuries. In some communities, where that usage is reclaimed, they are saying that if I use it, it immunizes me against its negative effects.

That is an example of a word that has fallen out of general conversation and literature into the realm of the unsayable. It’s quite different from the copulatory or excretory swearing in that it is so divisive. The great thing about the copulatory and excretory swearing is that they are common to the entire human race.

In the digital world, you can swear at someone without actually being face to face. Is this changing the way we curse? And what will swearing in tomorrow’s world look like?

One of the difficulties with swearing in online discourse is that there is no face-to-face repercussion, so it allows people to lash out without seeing the person that they’re speaking to as fully human. But it’s not swearing that is the problem. It’s possible to say someone is worth less as a human being based on their race, gender or sexuality using the most civil of language. For example, when Donald Trump called Hillary Clinton “a nasty woman” rather than using the c-word, most of us were able to break the code. We knew what he meant but because he hadn’t sworn it was seen as acceptable discourse.

In the future, I think that swearing will inevitably be reinvented; we’ve seen it change so much over the years. As our taboos change, that core of language that has the ability to surprise, shock or stun the emotional side of the brain will change, too. But I can’t predict where those taboos will go.

An implant that beams instructions out of the brain has been used to restore movement in paralysed primates for the first time, say scientists.

Rhesus monkeys were paralysed in one leg due to a damaged spinal cord. The team at the Swiss Federal Institute of Technology bypassed the injury by sending the instructions straight from the brain to the nerves controlling leg movement. Experts said the technology could be ready for human trials within a decade.

Spinal-cord injuries block the flow of electrical signals from the brain to the rest of the body resulting in paralysis. It is a wound that rarely heals, but one potential solution is to use technology to bypass the injury.

In the study, a chip was implanted into the part of the monkeys’ brain that controls movement. Its job was to read the spikes of electrical activity that are the instructions for moving the legs and send them to a nearby computer. It deciphered the messages and sent instructions to an implant in the monkey’s spine to electrically stimulate the appropriate nerves. The process all takes place in real time. The results, published in the journal Nature, showed the monkeys regained some control of their paralysed leg within six days and could walk in a straight line on a treadmill.

Dr Gregoire Courtine, one of the researchers, said: “This is the first time that a neurotechnology has restored locomotion in primates.” He told the BBC News website: “The movement was close to normal for the basic walking pattern, but so far we have not been able to test the ability to steer.” The technology used to stimulate the spinal cord is the same as that used in deep brain stimulation to treat Parkinson’s disease, so it would not be a technological leap to doing the same tests in patients. “But the way we walk is different to primates, we are bipedal and this requires more sophisticated ways to stimulate the muscle,” said Dr Courtine.

Jocelyne Bloch, a neurosurgeon from the Lausanne University Hospital, said: “The link between decoding of the brain and the stimulation of the spinal cord is completely new. “For the first time, I can image a completely paralysed patient being able to move their legs through this brain-spine interface.”

Using technology to overcome paralysis is a rapidly developing field:
Brainwaves have been used to control a robotic arm
Electrical stimulation of the spinal cord has helped four paralysed people stand again
An implant has helped a paralysed man play a guitar-based computer game

Dr Mark Bacon, the director of research at the charity Spinal Research, said: “This is quite impressive work. Paralysed patients want to be able to regain real control, that is voluntary control of lost functions, like walking, and the use of implantable devices may be one way of achieving this. The current work is a clear demonstration that there is progress being made in the right direction.”

Dr Andrew Jackson, from the Institute of Neuroscience and Newcastle University, said: “It is not unreasonable to speculate that we could see the first clinical demonstrations of interfaces between the brain and spinal cord by the end of the decade.” However, he said, rhesus monkeys used all four limbs to move and only one leg had been paralysed, so it would be a greater challenge to restore the movement of both legs in people. “Useful locomotion also requires control of balance, steering and obstacle avoidance, which were not addressed,” he added.

The other approach to treating paralysis involves transplanting cells from the nasal cavity into the spinal cord to try to biologically repair the injury. Following this treatment, Darek Fidyka, who was paralysed from the chest down in a knife attack in 2010, can now walk using a frame.